Olefin cyclodimerization to cyclobutanes is known in the art and is generally carried out by less efficient photochemical processes. The reaction comprises the [2+2] cyclo-addition of olefins to form the preferred cyclobutane product. However, the photochemical reaction suffers especially from low quantum efficiency. As a possible route to the production of cyclobutanes, the photochemical method for olefin cyclodimerization is also difficult to scale-up into an economically viable process. For example, norbornene, shown structurally herein as (I), is known to dimerize photochemically by [2+2] cyclo-addition to form pentacyclo [8.2.1.1.sup.4,7.0.sup.2,9.0.sup.3,8 ]-tetradecane (II). The dimer is also presented herein as the exo-trans-exo conformational isomer (IIa) and as the exo-trans-endo conformational isomer (IIb). However, the thermal conversion of norbornene to the dimer is unknown in the prior art. ##STR1##
Nonphotolytic olefin dimerizations catalyzed by transition metal catalysts are known but most do not produce cyclobutane derivatives. Activated dienes, however, can be easily cyclodimerized to cyclic dimers, such as the dimerization of norbornadiene (III) to pentacyclo [8.2.1.1.sup.4,7.0.sup.2,9.0.sup.3,8 ]-tetradecadiene-5,11 (IV). ##STR2##
R. H. Grubbs, et al. (J. Amer. Chem. Soc. 1978, 100, 7416) prepared cyclobutane from ethylene treated with tris(triphenylphosphene)tetramethylenenickel, but the yields were very low.
Bird, et al. (Tet. Lett., 1961,373) describe the production of norbornadiene dimer, pentacyclo [8.2.1.1.sup.4,7.0.sup.2,9.0.sup.3,8 ]-tetradecadiene-5,11, and related products by dimerization in the presence of certain metal carbonyl compounds, e.g., iron carbonyls, but in low yield.
Jolly, et al. (J. Chem. Soc. 1965, 6416), dimerized norbornadiene in contact with dicarbonyldinitrosyliron in near quantitative yield.
Cannel (U.S. Pat. No. 3,258,502) dimerized norbornadiene in contact with tetrakis(trihydrocarbylphosphite) nickel.
Arnold, et al., (J. Amer. Chem. Soc., 1965, 87, 2596) dimerized norbornene through irradiation of the cuprous chloride complex to produce (II) and dimerized norbornadiene in contact with hexacarbonylbis(triphenylphosphine)dicolbalt(O) to provide (IV). Six of the possible twelve stereoisomers of the dimers (II) and (IV) were prepared, separated and characterized.
In U.S. Pat. Nos. 4,827,064 and 4,827,073 to M. Wu, incorporated herein by reference, a unique catalyst system is reported for the preparation of superior hydrocarbon lubricants having low methyl to methylene branch ratio by oligomerization of alpha olefins using reduced valence state Group VIB metal oxide catalyst on porous support. The novel lubricant compositions (referred to as HVIPAO) comprise polyalpha-olefins. The method for their preparation employs as catalyst carbon monoxide reduced chromium on a silica support.
During the course of investigations relating to olefin copolymerization using the foregoing catalyst comprising reduced chromium on a silica support it was discovered that the catalyst is effective for the dimerization of norbornene (I).
Accordingly, it is an object of the present invention to provide a catalytic process for the thermal dimerization of cyclic olefins, particularly norbornene and norbornadiene.
Another object of the present invention is to provide a process for the dimerization of norbornene and/or norbornadiene in high yield and high stereoisomer selectivity.
A further object of the present invention is to provide a novel high energy fuel composition and process for preparing a novel high energy fuel.